Magnetic core



Dec. 7 1926. 1,609,745

r c. E. VAWTER MAGNETIC CORE Filed Jan. 4, 1924 INVENTOR ATTORNEY Patented Dec. 7, 1926.

UNITED STATES PATENT OFFICE.

CHARLES E. 'VAW'IEB, 0F PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO ELECTRAD, INC., 015 NEW YORK. N. Y.. A CORPORATION OF NEW YORK.

MAGNETIC GORE.

Application filed January 4, 1924. Serial No. 684,287.

This invention relates particularly to magnetic cores, the principa object of the invention being to provide a magnetic core which can be used to advantage in apparatus designed for high frequency work.

It is well known thatsolid iron cores cannot be used for applications involving the use of high frequency current due to the fact that the core losses dissipate an excessive amount of energy. These losses can be reduced .by using laminated cores, the effect of the laminations being to reduce the eddycurrent losses materially. But even this expedient is not a complete solution of the problem which arises when it is necessary to deal with high frequency currents, such as those of radio frequency. The most satisfactory cores that have been made heretofore, for use in high frequency circuits consist of finely divided magnetic material. such as iron dust, held together by a suitable binder. Such cores have been used to some extent in telephone loading coils. These cores, however, which are made by mixing the iron dust and a suitab'e binder to form a thick paste, and subsequently compressing the mixture, are not -wholly satisfactory when used in apparatus carrying currents of higher frequency than those encountered in telephone work. The chief reason for the fa lure of such cores to give wholly satisfactory results is that the particles of iron are not insulated from each other as they should be. The eddy-current losses, which increase as the square of the frequency, become excessive where the particles of iron are not insulated from each other to any greater extent than they are in these cores.

It might be supposed that suitab'emagnetic cores for high frequency work could 'be made by using an excess of the insulating binding agent so that the particles of iron would be completely insulated from each other. This procedure would undoubtedly result in the production of cores, the metallic particles of which are properly insulated from each other, but if these cores were made by simply using a large amount of the binding agent and drying the cores thoroughly, they would not be at all satisfactory, forthe intended purpose, The re- I have found that satisfactory magnetic.v

cores for high frequency work can be produced by thoroughly mixing a finely divrded ma etic substance, such as iron dust, with a re atively large quantity of insu'lating binding material, such as lacquer, and then extracting a portion of the lacquer from the mixture. The reason for extractmg a portion of the binding agent is to bring t e metal particles, which have previously been completely coated with the insulating material, into close proximity to each other; By this means, it is possible to press the metal particles together with the assurance that each of the particles is thoroughly coated with the insulating binding" agent. a condition which does not exist when 1ron dust and a binder are merely mixed together to form a thick paste. My improved process therefore consists inthoroughly coating each of the metal particles with the insulating material and then bringing these completely insu ated particles into close proximity toeach other. In this manner a ighly compacted core having high permeability and negligible core losses can be produced.

I will now describe in detail the particular method I prefer to employ in making my improved cores. It is tobe understood however that the details of this method may be modified without departing from the principle of the invention. The improved method and a particular application of the improved cores are illustrated in the accompanying drawings, in which- Fi 1 is a vertical section view of a variable inductance unit, in which the variation in inductance is produced by changing the position of a magnetic core with respect to a coil.

Fig. 2 is a transverse section taken on line 22 of Fig. 1, showing the construction of. the inductance unit of Fig. 1.

Fig. 3 is a longitudinal section view of a device whichcan be used making the improved cores,

Fi 3 shows a-quanti Huof paste 1 dispose within a tube 2. 's paste is made by mixing a finely divided ma etic substance with an insulating bin ng agent. The finel divided magnetic material may consist 0 iron dust or other finely divided metal such as nickel, cobalt and the Heusler alloys. I prefer to use iron, which can be made by reducing an oxide, for this material has a higher permeability than other metals. Regardless of the kind of metal used, it is necessary to have the metal in an extreme- Iy finely divided condition, for the smaller the particles the less will be the eddy-current loss. r

The binding agent which is mixed with the finel divided magnetic material may be shellac issolved in alcohol. Other binding agents may be used, such as pyralin, or a composition such as yralin mixed with shel lac can be used for is p11 ose. Itis quite important that enough of t e binding agent be used so that the particles of metal are each completely coated with thebindingagent.

I therefore prefer to use enoughof the binding agent so that the mixture of powdered material and binder forms a fluid composi'-' tion. I I The fluid composition referred to in the preceding paragraph is treated for the purpose of removing or extracting a portion of the binding agent with a view to bringingv the metal particles close together. This extraction process can be carried out in any desired manner, but I refer .to remove a portion of the binder. y compressing the mixture. The pressure serves a double purpose in that it squeezes out some of the liquid binding agent and at the same'time brings the metal particles into close proxe imity to each other.

The mixture of finely divided magnetic material and binding agent can be compressed in any suitable manner, and in Fig. 3 I have illustrated a simple device which can be used for this purpose. This device consists of a heavy protecting casing 3, pref: erably of metal, and adapted to receive the thin casing 2 which contains the mixture. The casing 2 may consist of insulating material such as fiber board. Other materials can be used for making the casing 2 but it is oftentimes desirable to use a fiber tube for this purpose, where it is desirable to leave the compressed material within the casing. The heavy casing 3 is provided with a screw threaded cap 4, and plungers 5 and 6 are provided at each end of this casing. These plungers are carried by rods 7 and 8 which have a screw-threaded connection with the bottom of the casing 3 and the cap 4, respectively. These plurilgersare just large enough to fit inside of e inner casing 2 and each of the plungers is provided with a plurality of perforations which perwithin the casing 2.

understood. .This operation can be continued until the desired amount of the binding agent has been removed from the mix- .ture, or in other words until the mixture has been compressed the desired extent. After the mixture has been compressed in this manner, the cap 4 can be removed and the inner casing 2 with its contents can be withdrawnffrom the outer casing 3. The magnetic material can be usedlas a core without removing it from, the ,casing 1-2, or this material may be removed fromflthe casing and sub ectedflto any desired foperations to form -it into a core"; The material may be: molded'into any shape, or it maybe sealed In Figs. l and 2 I haveshown a core,

made in the manner above-described, used as a means for varying the inductance of a coil 10 which is mounted on a panel 11. The coil is held in place by means of bolts 12 connected to the coil mounting 13 by means of nuts 14 screwed onto'the ends of the bolts. The bolts extend through the panelv 11 and may carry terminals 15 on the face of the panel. Spacers 16 are provided for the purpose of holding the coil mounting 13 the proper distance away from the panel 11.

The magnetic core comprises a casing 17 containing the magnetic material 18. made in the manner above described. The casing 17 is connected to a screw-threaded rod 19 which engages a nut 20 fixed to the panel 11. A knob 21 is provided at the free end of the rod 19. I prefer to make the container 17 for the magnetic core out of very thin material, and also to make the central part 21 of the coilmounting or support 13 out of very thin material, so that the magnetic core will be as close to the coil 10 as possible.

I have found that a variable inductance unit as described above possesses unique characteristics, in that extreme] ment of the inductance can e effected without dissipating any appreciable amount of electric ener V in the form of eddy-current and hysteresis losses. This type of core gives very satisfactory results when used in radio apparatus.

I claim:

1. The method of making which consists in mixing a finely divided magnetic substance and an insulating liquid sharp adjustmagnetic cores,

binding agent to form a fluid mixture, and subsequently extracting part of the insulating binding agent.

2. The method of making magnetic cores, which consists in mixing a finely divided magnetic substance and an insulating liquid binding agent to form a fluid mixture, and subsequentl extracting part of the insulating liquid y pressure.

3. The'method of making magnetic cores which consists in forming a fluid mixture by mixing a finely divided magnetic substance and an insulating liquid bindin agent which will harden upon drying, an extracting a portion of the binding agent by compressing the mixture. I

4. The method of making magnetic cores which consists in forming a' fluid mixture by mixing a finely divided magnetic substance and an insulating liquid binding agent which will harden upon drying, and extracting a portion of the binding agent by compressing the mixture and permitting the excess binding agent to escape through a sieve.

5. The method of making magnetic cores which consists in forming a fluid mixture by mixing a finely divided magnetic substance and an insulating liquid binding agent which will harden upon drying, placing the mixture in areceptacle, placing a sieve on top of the mixture and compressing the mixture by means of a perforated plunger until a portion of the binding agenthas been forced through the sieve and through the perforations in the plunger.

6. The method of making magnetic cores, which consists in mixing a finely divided magnetic substance and an insulating liquid binding agent to form a fluid mixture, and

tracting part of the insulating binding agent,

and compressing the mixture to substantially its ultimate density while extracting part of the remaining insulating binding agent.-

8. The method of making magnetic cores, which consists in mixing a finely divided magnetic substance and an insulating liquid binding agent to form a fluid mixture, and compressing the mixture to simultaneously extract part of the insulating binding agent and compress the mixture to its ultimate density.

9. The method of making magnetic cores, which consists in mixing a finely divided magnetic substance and an insulating liquid binding agent to form a fluid mixture, and completing the core by compressing the mixture in a mould in such a manner that part of the insulating binding agent is extracted while the mixture is being compressed to its ultimate density.

10. The method of making magnetic cores, which consists in mixing a finely divided magnetic substance and an insulating liquid binding agent to form a fluid mixture, and simultaneously extracting part of the in-. sulating bindinnagent and compressing the mixture to its u timate density to form the completed core.

In testimony whereof I afiix my signature. 7

CHARLES E. VAWTER. 

